Email domain invalid

Not a domain Synq sends from: reason says why: format, public_mailbox (gmail.com and such), reserved (for testing), synq_owned, or stage_suffix (preview takes only its test zone).

Field	Value
`code`	`email_domain_invalid`
`status`	422 Unprocessable Content
`title`	Email domain invalid

Synq's APIs answer errors with a problem document (RFC 9457, application/problem+json). Its type is the address of this page, and its code is email_domain_invalid. Branch on code, never on title or detail: a code never changes once it ships, while the words may.

{
  "type": "…/errors/email_domain_invalid",
  "title": "Email domain invalid",
  "status": 422,
  "code": "email_domain_invalid"
}

See every error code.